Why? Simple. First off, I've had that Hotmail account for, oh, 6 years now. Lots of mailing lists and websites whose mail I really DO want to get send there. My LJ is set up for that account. Everyone KNOWS that account. The reason I went to it in the first place was so I had an e-mail account that not only could I check no matter where I was, but that I didn't have to change if I changed ISPs. I've had shitloads of e-mail addresses over the years, and even if you cut out ISP e-mail addies, I've STILL had several. And, each time, it pissed me off enough to go somewhere else. Hotmail, for all that people say "it sucks" has never screwed me over, or screwed up my account in any way. Occasionally, I'll get a "server too busy" message, but that is rare, and, at best, a temporary situation.
Secondly, I don't fully trust GMail. I could give you plenty of reasons, but I'm gonna make it easy and say that I just think that GMail is too creepy. Now, I'm not saying that GMail is necessarily creepy in some way that Hotmail is not...but this is one case where I have a history with one, and not the other.
So, between the fact that I don't really trust them yet and the fact that I just don't want to go through the bullshit of changing over, no, I'm sticking with my Hotmail account. GMail is convenient for large files, but past that, I don't see me using it too extensively.